Arisu feels discomfort in her anus and, unable to endure it, visits the proctology department for an examination. However, the doctor in charge is an extreme pervert, an anal maniac obsessed with huge cocks. Moreover, all the nurses at the hospital are perverts as well, dragging Arisu into an increasingly dangerous situation. Enduring humiliation from her female peers, Arisu's anus is progressively violated and used as a sexual toy by the perverted doctor.